(a) Field of the Invention
The present invention relates to a method and a system for controlling acceleration torque of a hybrid vehicle. More particularly, the present invention relates to a method and a system for controlling acceleration torque of a hybrid vehicle that can pbe sufficient acceleration without imposing burden on a battery by changing a maximum torque of a vehicle according to environmental variables.
(b) Description of the Related Art
Recently, electric vehicles or hybrid vehicles have been developed and have attracted attention because of their enhanced fuel economy capabilities. While the electric vehicle generates driving torque of the vehicle only by a motor, the hybrid vehicle generates driving torque for the vehicle by an engine and a motor.
Typically, hybrid vehicles run in various modes (e.g., electric vehicle mode, hybrid mode, engine mode, and so on) according to a driving condition thereof. While in the electric vehicle mode, the driving torque is generated only by the motor. While in the hybrid mode, the driving torque is generated by the motor and the engine. And while in the engine mode, the driving torque is generated only by the engine.
Because the motor and the engine are operated together in the hybrid mode, torque division is very important for enhancing fuel economy and achieving a sufficient acceleration. Generally, when an acceleration torque is determined, the acceleration torque is divided between the engine and the motor according to a predetermined ratio.
For example FIG. 4 shows a conventional method for calculating the acceleration torque. FIG. 4 is a graph for explaining a conventional method for calculating an acceleration torque. As shown in FIG. 4, a minimum torque line and a maximum torque line are stored in a control portion. The minimum torque line is set by a creep torque according to a vehicle speed for achieving creep driving of a vehicle (driving at a D range without pushing an accelerator pedal). The maximum torque line is set by adding up a maximum torque of the engine and a maximum torque of the motor according to the vehicle speed. The minimum torque line and the maximum torque line do not change.
For instance, if the vehicle speed is 60 km/h, the maximum torque is 200 Nm and the minimum torque is −60 Nm. If a driver pushes the accelerator pedal and the position of the accelerator pedal is detected to be 50% at this state, the acceleration torque is calculated as follow.
                              acceleration          ⁢                                          ⁢          torque                =                ⁢                              (                                          maximum                ⁢                                                                  ⁢                torque                            +                              minimum                ⁢                                                                  ⁢                torque                                      )                    *                                                ⁢                  position          ⁢                                          ⁢          of          ⁢                                          ⁢          accelerator          ⁢                                          ⁢          pedal                                        =                ⁢                                            (                              200                -                60                            )                        *            0.5                    =                      70            ⁢                                                  ⁢            Nm                              
However, the maximum torques over a driving period that can be output from the engine and the motor are changed according to environmental variables. According to a conventional method for calculating the acceleration torque, effects of the environmental variables are not considered for calculating the acceleration torque. For example, when the vehicle runs at the hilly or mountainous sections, the maximum torque that can be output from the engine may be 50% of the predetermined maximum torque of the engine. Therefore, when the acceleration torque calculated by the conventional method is divided between the engine and the motor, it is difficult to maintain state of charge (SOC) of a battery.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.